Abstract

The site of the Kowyn's Pass rockfall shelter is situated on the road traversing the escarpment between Graskop and Bosbokrand in the northeastern Transvaal, South Africa. This route, on which the shelter is constructed, carries heavy traffic between the timber mills below the escarpment to Graskop Station as well as tourist traffic to and from the popular old gold-mining area of Pilgrim's Rest and the Kruger National Park.

The slope was subject to a major fall of rock in 1973 and further falls periodically blocked the pass after the suspect area was anchored. Ultimately, the Transvaal Provincial Roads Authority decided, towards the end of 1977, to construct a reinforced concrete rockfall shelter as a permanent and fail-safe protective measure. Construction of the structure, as shown in the main photograph, was complete in August 1980.

Selection of protective rockfall shelter as a permanent remedial measure

The geology of the rock face comprises basement Archaen granites outcropping at the road elevation. These are unconformably overlain by arkoses, lavas, siltstones and quartzites of the Dominion Reef Series. Following a detailed inspection of the 120 m high slope, four zones of unstable rock were identified, as shown stippled in Fig. 1, along a face length of 150 m. Within these zones unstable blocks, ranging from a few cubic metres in volume up to approximately 125 m3, were likely to fall. The major structural discontinuities forming these blocks were generally vertical with a trend perpendicular to the face. Occasional lineations strike along the

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